Refrigerating apparatus for continuously producing very low temperatures



Oct. 13, 1964 G. A. zoTos 3,152,457

REFRIGERATING APPARATUS FOR CONTINUOUSLY PRODUCING VERY LOW TEMPERATURES Filed Oct. 26, 1961 2 42 9 h g cow EXCHANGE/1 E (D E E 3 EXTERNAL WORK 0 U 20 A EXPANDER UNDER 4 g COOL/N6 2 EJECTOR 3 g COLD 2 9 J 8g EXCHANGE 32 HEAT TRANSFER MEANS U z @3 24 P3173 FIG. I g 28 To THROTTL/NG VALVE TEMPERATURE T FIG. 2

ENTROPY-- s INVENTOR. GEORGE .ZOTOS ATTORNEY United States Patent REFRIGERATING APPARATUS FOR CON- TENUOUSLY PRUDUCING VERY LOW TEMPERATURES George A. Zotos, Baltimore, Md., assignor to Martin- Marietta Corporation, Baltimore, Md., a corporation of Maryland Filed (Pet. 26, 1961, Ser. No. 147,866 7 Claims. (Cl. 62-500) This invention relates to cryogenic refrigeration systems and more particularly to an improved apparatus for the continuous undercooling of a compressed gas cryogen.

As is well known, the field of cryogenics is concerned with the production of Very low temperatures often considered within the region reached at the liquification of gases whose critical temperatures are below terrestrial temperatures. A wide variety of complex gas liquifiers are present in the history of the art, all having practical shortcomings when compared with a theoretically perfect refrigeration process. All must necessarily utilize an initial procedure for compressing and cooling a gaseous cryogen which is hereinafter referred to as the cooling function. Although a variety of components are found available for use within the cooling function of an apparatus, the conventional selection will include a compressor, purifying means, expansion means, thermal exchange components and complementing auxiliary circuits. The thermal exchange components conventionally are operable in complement with cool gases returned from a colder region of the overall cryogenic system.

Cooled gases developed within the above-noted cooling function of the cryogenic system are typically directed through an often intricate series of expansions and compressions devoted to the development of temperatures idealistically approaching absolute zero. It is this coldest portion of the system, hereinafter described as the undercooling function, to which the instant invention is directed. Existing cryogenic processes as typically developed by Claude, Collins, Schuftan, Kapitza and others utilize basically conventional cooling and under-cooling systems to achieve liquification of gases which, while attaining lower temperatures, are complex and bulky. The intricacies of the systems are founded upon a series of heretofore established basic considerations of achieving a stabilized cold balance or control of large temperature differentials and pressure balances in complement therewith throughout a system. For the most part, conventional cold producing arrangements have been devoted only to the production of liquified gases, the liquid being drawn from the end point of the system at or just beyond liquification. Laboratory efforts at adapting the existing processes to extremes of coldness beyond the function of mere liquified gas manufacture have produced systems of delicate complexity in maintaining an essential cold balance. The apparatus evolved from such complexity must of course suffer an attendant increase in space and weight demands as well as in power requirements. These demands are irreconcilable with industrial requirements for systems operable within the adverse environments found in airborne and space electronic applications where efiiciency, compactness, and weight become parameters of prime emphasis.

The instant invention uniquely provides a continuous, efficient and reliable system for obtaining regions of very low temperature. Its inherent simplicity allows adaptability to a wide variety of packaging arrangements, providing advantages in portability, low bulk and minimized weight. The invention is particularly characterized in utilizing ejector means to aid in re-evaporation of liquified or partially liquified gases within the undercooling function and to provide a gaseous recompression stage 3,152,457. Patented Oct. 13, 1964 while avoiding heat or other disturbing entropy increase discrepancies. It is a further object of the invention to utilize an ejector in common with expanded gases and evaporation means within the undercooling function to provide the lowest pressures of the system in the region where the lowest temperatures are produced. These and other objects of the invention are further described and illustrated by the following discussion and related drawings in which:

FIGURE 1 is a diagrammatic representation of the arrangement of basic components defining the invention, showing those within the cooling and undercooling functions.

FIGURE 2 presents a graph showing a Temperature- Entropy analysis of the refrigerating process.

Referring to the drawings, FIGURE 1 is illustrative of a generalized embodiment of the instant invention showing the arrangement of components for continuous cold environment production. Additionally, the elements are arranged to show their inclusion within the aforedescribed cooling and undercooling function of the system. To operate successfully at temperatures approaching absolute zero, gas cryogens available for use Within the system must be selected having appropriate physical characteristics. Illustrative of such gases are helium and hydrogen.

Within the cooling function, gas is suitably compressed within a compression stage shown generally at 10. Any of a myriad of such compression means and complementary auxiliary equipment familiar to the art are operable in the system, the choice of components being dependent upon power demands, packaging, and like characteristics. Gas leaving the compression stage 10 is directed by conduit 12 into a cold exchanger 14 where it is precooled preferably in out-of-contact counter-current thermal exchange with cooled gas conveyed from components within the undercooling function. Upon leaving cold exchanger 14, the cooled compressed gas exits from the conventional cooling function and enters Within the undercooling function of the system along conduit 12 to a junction 16. At junction 16, a portion of the gas enters conduit 17 and is directed to an expander 18 wherein work of expansion is extracted adiabatically to be disposed of within, but preferably out of, the domain of the cooling function of the system. Such disposal is indicated by arrow 20. One kind of expanding device operable with the arrangement is described in my co-pending application, Serial Number 107,148, filed May 2, 1961, entitled Cryogenic Expander. The remaining portion of gas leaving junction 16 enters an undercooler 24 from along conduit 22. Continuous, out of contact, countercurrent thermal exchange is effected as the gas traverses the undercooler and partial liquification of the gas may be expected during the progress of its transit. Undercooler 24 is provided cooled gas for the thermal exchange from expanding device 18 through a conduit 26. It may be noted that the temperature of the gases in transit within undercooler 24 may approach the lowest temperature prevailing within the expander 18. The use of the out of contact counter-current heat exchange is suggested as the prevailing most efficient mode of heat transfer, however, a variety of means are available to provide like performance. Gases within conduit 22 having been cooled or partially liquified within undercooling cold exchanger 24 are directed through an outflow control valve 28 into a conduit 36. Control valve 28 assumes the task of securing or stabilizing the partial liquification of gas in transit within undercooler 24. The partially liquified gas within conduit 30 enters an undercooling region 32, which may be a cold sink, devoted to the ultimate function of the refrigerating system. It is here that the lowermost temperatures of the cycle are reached for use in supplying a continuous cold environment to operational units as electronic systems and the like. The region may assume any of a variety of configurations directed to the mode of heat transfer required by the industrial application at hand. It is preferred that no accumulation of liquids is made at region 32, as the region is devoted to a continuous and complete re-evaporation of the liquids entering it from conduit 30. In suitable gastight connection with region 32, an exhaust conduit 34 draws re-evaporated gas vapors from the region into the suction inlet of an ejector 36. Ejector 36, operable in a conventional Venturi exhaust pumping mode, is powered from conduit 38 by gas conducted from the expanded gas chambers of undercooler 24. A somewhat precise control of gas pressures entering the ejector must be maintained in order to assure an appropriate cold balance within the undercooling and cooling functions, in addition to providing acceptable operation of the ejector. Such pressure requirements may be realized by suitable regulation of outflow gas pressure from expander 18. Control is effected by adjustment of operational factors as inlet-outlet diameter and position arrangements and like procedures familiar to the fiuid mechanical art. Contrary to a priori prediction, a cold balance is maintainable at very low temperature while utilizing at the ejector the saturated vapors from region 32 in combination with an expanded gas input from conduit 38 to achieve a recompression of the gases and consequent ejector output temperature below that entering the initial expansion phase at conduit 17. Prior art teachings have heretofore advised that such reduced output temperatures are unattainable in consonance with a stabilized cold balance. Gas deriving from ejector 36 is conducted from within conduit 40 into the cooling function of the system where it is utilized for the purpose of counter-current thermal exchange within cold exchanger 14. From cold exchanger 14 a conduit 42 returns the gas into the compression phase It) to complete the overall refrigeration cycle in continuous and uninterrupted fashion. Noteworthy of the system above described is the unique elimination of pumping devices and similar mechanical contrivance having power supplies derived from exterior sources for undercooling use.

Typically, the point of lowest pressure in a refrigeration system is at the input stage of the compressor. In the practice of this invention lowest pressures within the system are produced at a point more remote from the compressor without the utilization of an auxiliary compressor powered by exterior means. The recompressing ejector, as is shown, operates under the power input of gases exhausting from the expander.

The system is further portrayed with reference to the generalized Temperature-Entropy (T-S) diagram of FIGURE 2 which may also be read in conjunction with FIGURE 1. Referring to the diagram, realistic temperatures and equi-pressure curves are denoted in solid lines whereas theoretical performance is described along dotted lines. For clarity, certain of the component numbers shown in FIGURE 1 are reproduced in the T-S diagram having a suffix a.

Cooling equi-pressure line P is representative of the operation of the system from initial compression 1th: through the undercooler to the outflow control valve at 28a. Equi-pressure line P is representative of the functioning of the system from expansion 18a through thermal exchange within the undercooler to the driving nozzle of the ejector 3611. As depicted, pressure P, is maintained at a higher level than P Expansion occurs from the expander input temperature T to lowered output temperature T theoretically optimum expansion being denoted by a vertical dotted line. In conformity with the art utilizing isotropic expansion to effect gas liquification, the equi-pressure curves P through R; intersect and define saturation lines dotted and shown generally at 50, 51, and 52. Since a partial liquification is produced within the system, the saturation line must assume a configuration showing a predominance of gas within the region at St and a predominance of liquid within the region at 51. Equi-pressure line P displays the pressure within re-evaporation region 32, the vapors from which region are directed into the suction mode of the ejector. Contingent upon suitable design conditions within region 32, the pressure P within that region is dependent upon the corresponding saturation temperature T the level of which is shown as ideal by dotted lines at 51 or it may be described at the level of the realistic backflow pressure shown at 52 as an extension of pressure P hereinafter described. In view of the inter-mingling of gases having pressures P and P within the ejector, temperatures within that component will fall within a range shown between 36a and 34a. The conclusive effort of the ejector in recompressing gases within region 32 is denoted by equi-pressure curve P whereat the very influential temperature level T is evolved. Since gases at pressure P and temperature T are devoted to thermal exchange cooling of initially compressed gases within cold exchanger 14, it becomes essential that pressure P be high enough to drive gases released from region 32 and attain the back pressure P to the cooling function of the system. It is most essential in attaining an operative cold balance within the thermodynamics of the system, that the temperature T following recompression, does not exceed temperature T leaving the cold exchange system within the cooling function. Under the arrangement of components within the system as above described, the refrigerating system is operative at relatively high thermal efficiencies despite the fact that recompression is effected by means of an ejector within the undercooling function. A particular advantage of the system lies in the elimination of the requirement for substantial quantities of liquified gases within the cooling environment region 32, making the system adaptable for applications wherein the characteristics of gases would induce impediments within the refrigerative cycle. The system as above described evidences a high reliability in applications where complete independence of gravitational or accelerative conditions is essential.

Through the unique provisions as above described a cryogenic refrigerative system is furnished having advantages of reliability, etficiency, and compactness. Although the invention has been described by making reference to a schematic representation, such representation is to be understood in an instructive rather than a restrictive sense, many variants being possible within the scope of the claims hereunto appended.

I claim:

1. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprismg:

(1) a compressor for compressing said cryogen and pump it through said refrigeration system, said compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connected to receive precooled cryogen from said cold exchanger for expanding said cryogen and for extracting work therefrom;

(4) a branch conduit connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool said diverted portion;

(6) valve means providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough;

(7) gas recompression means connected to receive and recompress undercooled cryogen from said valve means said recompression means being operable in response to gases expanded in said expander and exhausting said recompressed gas into said low pressure inlet of the compressor in a manner providing for said precooling, thereby establishing the lowest pressure within said system intermediate said recompression means and valve means; and

(8) heat transfer means intermediate said recompression means and said valve means for providing a cooling region.

2. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprismg:

(l) a compressor for compressing said cryogen and pumping it through said refrigeration system, said compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connected to receive precooled cryogen from said cold exchanger for expanding said cryogen and for extracting work therefrom;

(4) a branch conduit connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool said diverted portion;

(6) valve means providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough;

(7) an ejector having a power inlet influid communication to receive expanded cryogen from said expander and said undercooling cold exchanger, a suction inlet connected to receive undercooled cryogen deriving from said valve means, and an exhaust connected to return said cryogen to said low pressure inlet of the compressor in a manner providing for said precooling, thereby establishing the lowest pressure within said system intermediate said suction inlet and valve means; and

(8) heat transfer means intermediate said ejector and said valve means for providing a cooling region.

3. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprising:

(1) a compressor for compressing said cryogen and pumping it through said refrigeration system, said compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connected to receive precooled cryogen from said cold exchanger for expanding said cryogen and for extracting Work therefrom;

(4) a branch conduit connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool and partially liquify said diverted portion;

(6) valve means providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough, thereby stabilizing said partial liquification of the diverted por tion of cryogen;

(7) an ejector having a power inlet in fluid communication to receive expanded cryogen from said expander and said undercooling cold exchanger, a suction inlet connected to receive undercooled cryogen deriving from said valve means, and an exhaust connected to return said cryogen to said low pressure inlet of the compressor in a manner providing for said precooling thereby establishing the lowest pressure within said system intermediate the ejector and valve means; and

(8) heat transfer means intermediate said ejector and said valve means for providing a cooling region.

4. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprismg:

(1) a compressor for compressing said cryogen and pumping it through said refrigeration system, said compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connected to receive precooled cryogen from said cold exchanger for expanding said cryogen and for extracting work therefrom;

(4) a branch conduit connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool said diverted portion;

(6) valve means providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough;

(7) gas recompression means powered by the flow of expanded cryogen exhausted from said expander and said undercooling cold exchanger to receive and recompress undercooled cryogen deriving from said valve means and to exhaust said recompressed gas into said low pressure inlet of the compressor in a manner providing for said precooling; and

(8) a cold sink in connection between said valve means and said gas recompression means to receive cryogen passing through said valve means, thereby establishing the lowest pressure within said system within said cold sink.

5. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprismg:

(1) a compressor for compressing said cryogen and pumping it through said refrigeration system, said compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connected to receive precooled cryo gen from said cold exchanger for expanding said cryogen and for extracting work therefrom;

(4) a circuit branch connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool and partially liquify said diverted portion;

(6) a Venturi ejector having a suction inlet, a power inlet in fluid communication with expanded cryogen from said expander and said undercooling cold exchanger, and an exhaust in fluid communication to return said cryogen to the low pressure inlet of said compressor in a manner providing for said precoola;

(7) a throttle valve providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough;

(8) a cold reservoir connected to receive the cryogen passing through said throttle valve; and

(9) a conduit connecting said reservoir to the suction inlet of said ejector to exhaust said reservoir, thereby eifecting the evaporation of said partially liquified Z cryogen and establishing within said cold reservoir the lowest pressure of cryogen within said system.

6. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprising:

(1) a compressor for compressing said cryogen and pumping it through said refrigeration system, said compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connected to receive precooled cryogen from said cold exchanger for expanding said cryogen and for extracting work therefrom;

(4) a circuit branch connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool said diverted portion;

(6) a Venturi ejector having a suction inlet, a power inlet in fluid communication with expanded cryogen from said expander and said undercooling cold exchanger, and an exhaust in fluid communication to return said cryogen to the low pressure inlet of said compressor in a manner providing for said precools;

(7) a throttle valve providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough;

(8) a cold reservoir connected to receive the cryogen passing through said throttle valve; and

(9) a conduit connecting said reservoir to the suction inlet of said ejector to exhaust said reservoir, thereby establishing within said reservoir the lowest pressures and temperatures of cryogen within said system.

7. A continuously operable cryogenic refrigeration system for the circulation therein of a gas cryogen comprising:

(1) a compressor for compressing said cryogen and pumping it through said refrigeration system, said 8 compressor having a low pressure inlet and a high pressure output;

(2) a cold exchanger receiving compressed cryogen from said high pressure output for precooling said cryogen;

(3) an expander connectedto receive precooled cryogen from said cold exchanger for expanding said cryogen and for extracting work therefrom;

(4) a circuit branch connected to divert a portion of the cryogen from passing into said expander;

(5) an undercooling cold exchanger providing a thermal bond between said diverted portion of said cryogen and the expanded cryogen from said expander to undercool and partially liquify said diverted portion;

(6) a Venturi ejector having a suction inlet, a power inlet in fluid communication with expanded cryogen from said expander and said undercooling cold exchanger, and an exhaust in fiuid communication to return said cryogen to the low pressure inlet of said compressor in a manner providing for said precools;

(7) a throttle valve providing a restricted controlled orifice connected to transmit the diverted undercooled portion of said cryogen therethrough;

(8) a cold reservoir connected to receive the cryogen passing through said throttle valve; and

(9) a conduit connecting said reservoir to the suction inlet of said ejector to exhaust said reservoir and evaporate said partially liquified portion of cryogen, thereby establishing within said reservoir the lowest pressures and temperatures of cryogen within said system.

References Cited in the file of this patent UNITED STATES PATENTS 1,264,807 Jeir'eries Apr. 30, 1918 1,901,389 Hazard-Flamand Mar. 14, 1933 2,957,318 Morrison Oct. 25, 1960 FOREIGN PATENTS 831,613 Great Britain Mar. 30, 1960 

1. A CONTINUOUSLY OPERABLE CRYOGENIC REFRIGERATION SYSTEM FOR THE CIRCULATION THEREIN OF A GAS CRYOGEN COMPRISING: (1) A COMPRESSOR FOR COMPRESSING SAID CRYOGEN AND PUMP IT THROUGH SAID REFRIGERATION SYSTEM, SAID COMPRESSOR HAVING A LOW PRESSURE INLET AND A HIGH PRESSURE OUTPUT; (2) A COLD EXCHANGER RECEIVING COMPRESSED CRYOGEN FROM SAID HIGH PRESSURE OUTPUT FOR PRECOOLING SAID CRYOGEN; (3) AN EXPANDER CONNECTED TO RECEIVE PRECOOLED CRYOGEN FROM SAID COLD EXCHANGER FOR EXPANDING SAID CRYOGEN AND FOR EXTRACTING WORK THEREFROM; (4) A BRANCH CONDUIT CONNECTED TO DIVERT A PORTION OF THE CRYOGEN FROM PASSING INTO SAID EXPANDER; (5) AN UNDERCOOLING COLD EXCHANGER PROVIDING A THERMAL BOND BETWEEN SAID DIVERTED PORTION OF SAID CRYOGEN AND THE EXPANDED CRYOGEN FROM SAID EXPANDER TO UNDERCOOL SAID DIVERTED PORTION; 